服役环境下燃料电池用质子交换膜疲劳裂纹扩展规律研究

As a clean and high-efficiency energy technology, proton exchange membrane fuel cell is a promising candidate as a power source for electric vehicles. However, its commercialization, to a large extent, is hindered by the durability of proton exchange membrane. The proton exchange membrane keeps working for 40-50% of whole lifetime after the detection of cracks during fuel cell practical operating condition. Nevertheless, the fatigue crack propagation behavior of proton exchange membrane is scarcely investigated. Hence, the objective of this project is to explore the roles of inner (chemistry) and outer (reinforcement) factors in controlling fatigue crack propagation behaviors of proton exchange membranes as well as their microscopic deformation mechanisms through investigating the fatigue crack propagation behaviors of Aquivion short side-chain membrane and Nafion XL reinforced composite membrane. Considering practical operating conditions of fuel cells, the impacts of temperature, relative humidity and stress ratio on fatigue crack propagation behaviors of aforementioned proton exchange membranes will also be explored, in the hope of clarifying the roles of temperature and relative humidity in controlling fatigue crack propagation behaviors as well as the extent of such impacts. The relationship between fatigue crack propagation rates and fuel cell practical operating parameters will also be established based on stress analysis arising from temperature and relative humidity changes. The achievements of this project will serve as the theory fundamentals for proton exchange membrane optimization as well as new membrane development.

质子交换膜燃料电池作为一种新型高效清洁能源技术，有望作为动力源广泛应用于电动汽车。但其商业化推广却很大程度上受制于质子交换膜的耐久性。在燃料电池实际运行工况下，质子交换膜出现裂纹后仍有40-50%的寿命。尽管如此，质子交换膜的疲劳裂纹扩展规律却鲜有研究。因此，本课题通过研究Aquivion短侧链质子交换膜和Nafion XL机械增强质子交换膜的疲劳裂纹扩展规律，探究材料内（化学结构）外（机械增强）因素对质子交换膜疲劳裂纹扩展规律及微观变形机制的影响。考虑燃料电池实际运行工况，考察温湿度环境和应力比等运行工况参数对上述质子交换膜疲劳裂纹扩展规律的影响，阐明温度和湿度的作用机制和影响程度。基于对质子交换膜温湿度变化产生的应力分析，建立疲劳裂纹扩展速率与燃料电池实际运行工况间的联系，从而为质子交换膜的优化设计和新型质子交换膜的开发提供理论支撑。

质子交换膜燃料电池作为动力源广泛应用于交通运输等领域，其中质子交换膜作为其核心部件，其结构完整性对于保证燃料电池的性能和耐久性至关重要。在服役工况下，质子交换膜出现裂纹后仍有40-50%的寿命。本课题围绕质子交换膜的疲劳裂纹扩展性能，探究了温湿度环境、材料化学结构、机械增强层等因素对质子交换膜疲劳裂纹扩展规律及失效机制的影响。研究内容和主要研究成果如下：（1）探明了不同温湿度环境下Nafion 212质子交换膜的疲劳裂纹扩展规律，揭示了温度和湿度对质子交换膜疲劳裂纹扩展的影响机理。（2）澄清了机械增强层、成型工艺和化学结构（短侧链长度）等因素对燃料电池膜疲劳裂纹扩展的影响规律和机理，揭示了Nafion XL机械增强质子交换膜裂纹尖端应力和环境耦合促进裂纹扩展机制。（3）基于时-温叠加原理，建立了基于Arrhenius公式的疲劳裂纹扩展速率表达式，成功地预测了各温度下的疲劳裂纹扩展速率。同时，基于考虑循环损伤的内聚力模型，较好地预测了更接近真实工况双轴载荷下燃料电池膜的疲劳裂纹扩展行为。研究成果将增进对质子交换膜疲劳破坏机理和机械耐久性的理解，从而为质子交换膜的优化设计和新型质子交换膜的开发提供理论支撑。